There are a couple of free programs that are fairly comprehensive and compatible with AutoCAD. They were mentioned on a computer forum I visit a couple of days ago. Try a Google search and I'll try to resurrect the names.

I taught myself AutoCAD, but Sketchup is incomprehensible to me. Go figure.

__________________
"The great object is, that every man be armed. Everyone who is able may have a gun." - Patrick Henry